The present invention relates to a vehicle power door lock actuator. More particularly, the present invention relates to a power door lock actuator that operates quietly, has substantially zero back drive and can be mounted on all vehicle types without extra tooling for each type vehicle.
Standard door lock systems include a manual door lock button, a key entry, a locking mechanism and a connecting rod for interconnecting the button, key entry and locking mechanism. By manually pulling or pushing the locking button or operating the key entry, the door can be locked or unlocked.
Power door lock actuators of the general type do the pushing or pulling of the locking mechanism by the flip of a switch. Generally, the power actuator has an electric motor coupled to an output member that is connected to the door lock system. When the motor is energized, the output member is driven to automatically lock or unlock the door. An example of a common door lock actuator is disclosed in U.S. Pat. No. 3,954,016 of which the Applicant of the present invention was a co-inventor. The disclosed actuator has an output member 11 attached at one end to a manually-operated push button 28 with a rack section 100 at the other end connected to a motor 32 through a pinion gear 88. When motor 32 is energized at switch 90, the output member 11 extends or retracts in a linear path with respect to housing 31 to lock or unlock the door. A concentric guide roller 74 is provided to maintain proper alignment of the pinion gear 88 with respect to rack section 100.
Ideally, a power actuator should operate quietly and allow easy manual operation of the lock system. Although ideal, in actual practice quiet operation and easy manual operation are for the most part mutually exclusive. Quiet operation is obtained at the expense of manual operation, while easy manual operation is obtained at the expense of quiet operation.
A power actuator can be designed to operate quietly. This is typically accomplished by having a large gear ratio between the motor and output arm which slows down the movement of the system, thereby reducing noise. By slowing the speed of actuation, sudden impact of the door lock and actuator mechanisms are eliminated reducing noise and damage to the system. The disadvantage to using a large gear ratio is the resistance it gives to manual operation. This resistance to manual operation of the actuator is commonly referred to as "back-drive" which ideally should equal or at least closely approach zero. With zero back-drive, there is no resistance to manual operation of the door locks due to the actuator.
Back-drive can be reduced in the door lock actuator by using a small gear ratio or direct drive between the motor and the output arm. A disadvantage to this design is an increase in the speed of operation resulting in louder operation noises and damage to the system. Although back-drive is reduced, the actuator is louder. Another disadvantage to using smaller gear ratios or direct drive is the need for a larger motor to provide the necessary torque to operate the lock system. Larger motors weigh more, pull greater amperage, require larger, more costly wiring, necessitate the use of a relay and can encounter voltage drop problems.
The problem of back-drive is also related to magnetic cogging of the motor and the gear ratio of the actuator. Cogging is the resistance that is due to the magnetic flux of the electric motor resisting rotation of the rotor past the magnetic field. Cogging will vary with the size of the motor and its effect on manual operation will be amplified by the gear ratio used. With a smaller motor, the magnetic field is smaller; however, a larger gear ratio is needed to operate the system. The increased gear ratio increases resistance to manual operation because it effectively increases the cogging of the electric motor. A larger motor inherently has increased cogging and even though the cogging is not further amplified by the gear ratio, it contributes to back-drive.